We don't know. BGR originally posted that it had, but has updated with a comment from Sling PR saying they haven't heard from Apple one way or another yet.
While SlingPlayer was submitted quite a while ago, all we have right now are questions. Bandwidth is likely a concern for AT&T. Sure, they've had other devices running Sling Player for years, but suddenly dropping 10 million odd iPhones streaming video into the mix is a non-trivial concern from their perspective -- remember their quickly rescinded "new terms of service".
However, we're still keeping our fingers crossed. YouTube app runs off 3G, after all, and while Ustream was forced to be WiFi only for now, Sling Player should at least have that option over flat out rejection.
Or do we the people demand our Sling over 3G now? (Even if we have to still get a new SlingBox to enjoy it...)